Recumbirostran ‘microsaurs’ are not amniotes
Bibliographic record
Abstract
Amniota is a tetrapod clade that includes extant mammals and reptiles, including birds, as well as a wealth of extinct taxa extending over 318 million years of Earth’s history. For over three decades, Amniota has been treated as a crown group, but the content of stem amniotes has varied among large-scale analyses of Palaeozoic tetrapods. Nine recent phylogenetic studies on Palaeozoic tetrapods, all derived from each other, have potentially changed our perspectives on amniote origins and early evolution. The first of these analyses posited that two particular clades of Palaeozoic tetrapods, Recumbirostra and Lysorophia, both previously considered to be lepospondyl stem-amniotes, are actually amniotes. This raises the possibility that early amniotes included both small fossorial and terrestrial animals, some of which show strong evidence of limb reduction. Here we show that the strange position of these small, often fossorial and limb-reduced tetrapods in Amniota is the result of two fundamental flaws: (1) the phylogenetic analysis combines two separate data matrices that were each designed to test only patterns of relationships among early anamniote tetrapods; and (2) the absence of key amniote characters. Our reanalysis of Palaeozoic tetrapod interrelationships reinstates recumbirostrans and lysorophians outside Amniota. The results of our study impact other recent studies that have simply accepted the codings in the data matrix that resulted in the hypothesis that recumbirostrans are amniotes and raises important questions about the initial diversification of amniotes and the evolution of fossoriality and limb reduction among tetrapods.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".